Control System of Internal Combustion Engine

ABSTRACT

A cylinder air filling amount is divided into a first amount of air and a second amount of air, the first amount of air and the second amount of air are calculated, and the first amount of air and the second amount of air are totaled to calculate a cylinder air filling amount. The first amount of air is the excess of the cylinder air filling amount with respect to the throttle valve air passage amount occurring due to an intake stroke being performed. The drop in intake pressure occurring due to an intake stroke being performed is detected for each cylinder and the total value of the intake pressure drop in a 720° crank angle range is calculated. The first amount of air is calculated based on an intake pressure drop and the intake pressure drop total value. Due to this, it is possible to simply and accurately calculate a cylinder air filling amount.

TECHNICAL FIELD

The present invention relates to a control system of an internalcombustion engine.

BACKGROUND ART

Regarding an internal combustion engine provided with a plurality ofcylinders, introducing air into an intake pipe extending from a throttlevalve to an intake valve through the throttle valve in exactly athrottle valve air passage amount, and discharging air from the intakepipe through an intake valve in exactly a cylinder air filling amount tofill a cylinder at the time of an intake stroke, known in the art is acontrol system of an internal combustion engine wherein a formulaobtained from the Law of the Conservation of Mass for the intake pipeand a state equation for the air in the intake pipe is used to calculatethe cylinder air filling amount of the cylinder (see Japanese PatentPublication (A) No. 2002-70633).

To use the above formula to calculate a cylinder air filling amount, forexample, the temperature of the air in the intake pipe and the volume ofthe intake pipe have to be found. However, to find the air temperature,for example, not only is a temperature sensor necessary, but also, ifconsidering the response delay, even if using a temperature sensor, itwould be difficult to accurately find the air temperature. Further, theintake pipe includes manufacturing error, so the volume of the intakepipe cannot be considered equivalent to, for example, the design value.Measurement of the volume for each intake pipe is also extremelyimpractical.

Further, when using a formula to estimate a cylinder air filling amount,if using a formula obtained based on the Law of the Conservation of Massand state equation as it is, the formula would become complicated andthe calculation load would become huge, so normally this formula issimplified for use. Here, if the intake valve opening/closing timing isset to the retarded side, an intake valve will remain open even afterintake bottom dead center. In this case, even if the piston starts torise, since the intake valve is held in the open state, the air suckedinto the cylinder is liable to flow back into the intake pipe. However,if simplifying the formula for use when estimating the cylinder airfilling amount as explained above, this backflow of air is notconsidered and therefore the calculated cylinder air filling amount endsup including error.

DISCLOSURE OF THE INVENTION

Therefore, the present invention has as its object to provide a controlsystem of an internal combustion engine able to simply and accuratelycalculate a cylinder air filling amount.

The present invention provides as means for solving this problem acontrol system of an internal combustion engine as set forth in theclaims.

To solve this problem, in a first aspect of the invention, there isprovided a control system for an internal combustion engine providedwith a plurality of cylinders, introducing air into an intake passagepart extending from a throttle valve to an intake valve through thethrottle valve in exactly a throttle valve air passage amount, anddischarging air from the intake passage part through an intake valve inexactly a cylinder air filling amount to fill a cylinder at the time ofan intake stroke, wherein the cylinder air filling amount is dividedinto a first amount of air and a second amount of air, the first amountof air being an excess of a cylinder air filling amount with respect toa throttle valve air passage amount occurring due to an intake stroke,wherein the control system comprises an intake pressure drop detectingmeans for detecting a drop in intake pressure occurring due to an intakestroke being performed for each cylinder; a first air amount calculatingmeans for calculating the first amount of air for a cylinder based onits intake pressure drop; a throttle valve air passage amount detectingmeans for detecting a throttle valve air passage amount; a second airamount calculating means for calculating the second amount of air for acylinder based on the throttle valve air passage amount; a cylinder airfilling amount calculating means for totaling the first amount of airand the second amount of air to calculate the cylinder air fillingamount for a cylinder; and a control means for controlling the enginebased on the cylinder air filling amount of the cylinder, and whereinthe first air amount calculating means sets a set crank angle range soas to include the intake strokes of at least two cylinders for whichcylinder air filling amounts are to be calculated, calculates the totalvalue of the intake pressure drop of the cylinders performing an intakestroke in the set crank angle range, and calculates the first amount ofair based on each intake pressure drop and the intake pressure droptotal value.

Further, in a second aspect of the invention, there is provided thefirst aspect of the invention wherein when backflow of air from inside acylinder to the intake passage part occurs at the end of an intakestroke, the action of the second air amount calculating meanscalculating the second amount of air is prohibited.

To solve the above problem, in a third aspect of the invention, there isprovided a control system for an internal combustion engine providedwith a plurality of cylinders and a plurality of intake valves, whereinthe cylinder air filling amount to a cylinder is divided into a basicamount of air and an excess amount of air flowing from an intake passagepart to the inside of the cylinder exceeding a throttle valve airpassage flow rate due to opening of an intake valve, and wherein thecontrol system comprises a basic air amount calculating means forcalculating a basic air amount based on a throttle valve air passageflow rate of air flowing into the intake passage part through thethrottle valve and the opening time of each intake valve; an excess airamount calculating means for calculating an excess air amount based onthe drop in intake pressure due to opening of the intake valve; acylinder air filling amount calculating means for totaling the basic airamount and excess air amount to calculate a cylinder air filling amountto a cylinder; and a control means for controlling the engine based onthe cylinder air filling amount to a cylinder, and wherein the basic airamount calculating means calculates a virtual intake valve opening timeso that the average air flow rate to all cylinders becomes equal to thethrottle air passage flow rate and uses the virtual intake valve openingtime as the opening time of an intake valve.

According to the third aspect of the invention, the virtual intake valveopening time becomes a value by which the average air flow rate to allcylinders becomes equal to the throttle air passage flow rate. For thisreason, when there is backflow of air from inside a cylinder to theintake pipe, the virtual intake valve opening time becomes shorter thanthe actual intake valve opening time. If this virtual intake valveopening time is used by the basic air amount calculating means tocalculate the basic air amount, the basic air amount can be accuratelycalculated.

Further, in a fourth aspect of the invention, there is provided thethird aspect of the invention wherein the basic air amount calculatingmeans uses the virtual intake valve opening time as the opening times ofthe intake valves when backflow of air to the intake passage part occursnear the intake valve opening timing or near the intake valve closingtiming.

According to the present invention, the cylinder air filling amount canbe simply and accurately calculated.

The present invention will be more fully understood from the drawingsand the description of preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a view of an intake valve opening/closing timing.

FIG. 3 is a view of the results of detection of an intake pressure Pm.

FIG. 4 is a time chart for explaining an intake pressure drop ΔPmdwni.

FIG. 5 is a view for explaining a method of calculation of a cylinderair filling amount Mci.

FIG. 6A and FIG. 6B are time charts for explaining a method forcalculation of a parameter Km.

FIG. 7A and FIG. 7B are time charts for explaining another example of amethod for calculation of a parameter Km.

FIG. 8 is a time chart for explaining a cylinder intake air flow ratemci when an intake valve opening/closing timing is set to a retardedside.

FIG. 9 is a flow chart showing a routine for calculation of a fuelinjection time TAUi.

FIG. 10 is a flow chart showing a routine for calculation of a cylinderair filling amount Mci for a first embodiment.

FIG. 11 is a time chart for explaining error in approximation.

FIG. 12A and FIG. 12B are time charts for explaining a method ofcalculation of a virtual intake valve opening time x.

FIG. 13 is a time chart for explaining a method of calculation of thevirtual intake valve opening time x.

FIG. 14 is a flow chart showing a routine for calculation of a cylinderair filling amount Mci for a second embodiment.

FIG. 15 is a flow chart showing the routine for calculation of the valueof a variable x.

BEST MODE FOR WORKING THE INVENTION

Below, embodiments of the present invention will be explained in detailwith reference to the drawings. FIG. 1 show the case of application ofthe present invention to a four-stroke cylinder injection type sparkplug ignition type internal combustion engine. Note that the presentinvention may also be applied to another spark plug ignition typeinternal combustion engine or a compression ignition type internalcombustion engine as well.

As shown in FIG. 1, in the present embodiment, an engine body 1 providedwith, for example, eight cylinders is provided with a cylinder block 2,pistons 3 reciprocating in the cylinder block 2, and a cylinder head 4fixed on the cylinder block 2. Between each piston 3 and the cylinderhead 4, a combustion chamber 5 is formed. The cylinder head 4 isprovided with, for each cylinder, an intake valve 6, intake port 7,exhaust valve 8, and exhaust port 9. Further, as shown in FIG. 1, at thecenter of the corresponding part of the inside wall of the cylinder head4, a spark plug 10 is provided. Near the inside wall of the cylinderhead 4, a fuel injector 11 is provided. Further, the piston 3 is formedat its top surface with a cavity 12 extending from below the fuelinjector 11 to below the spark plug 10.

The intake port 7 of each cylinder is connected through an intake branchtube 13 to a surge tank 14. The surge tank 14 is connected through anintake pipe 15 to an air cleaner 16. Inside the intake pipe 15 isprovided a throttle valve 18 driven by a step motor 17. Note that inthis description, the part of the intake passage including the intakepipe 15 downstream of the throttle valve 18, surge tank 14, intake tube13, and intake port 7, that is, the part of the intake passage from thethrottle valve 18 to the intake valve 6, will be called the “intake pipepart IM”. On the other hand, the exhaust port 9 of each cylinder isconnected through the exhaust branch tube and exhaust pipe 19 to anexhaust purification device 20 built in a catalytic converter 21. Thiscatalytic converter 21 is communicated with the atmosphere through amuffler (not shown).

The intake valve 6 of each cylinder is driven to operate by an intakevalve drive system 22. This intake valve drive system 22 is providedwith a cam shaft and a switching mechanism for selectively switching arotational angle of the cam shaft to an advanced side and a retardedside with respect to the crank angle. When the rotational angle of thecam shaft is advanced, as shown by AD in FIG. 2, the opening timing VOand closing timing VC of the intake valve 6 are advanced, therefore theopening/closing timing is advanced. On the other hand, when therotational angle of the cam shaft is retarded, as shown by RT in FIG. 2,the opening timing VO and closing timing VC of the intake valve 6 areretarded and, therefore the opening/closing timing is retarded. In thiscase, the amount of lift and working angle (opening time interval) ofthe intake valve 6 are maintained and the phase angle (opening timing)is changed. In the internal combustion engine shown in FIG. 1, therotational angle of the cam shaft is switched to the advanced side orthe retarded side in accordance with the engine operating state. Notethat the present invention can be applied as well when the openingtiming of the intake valve 6 is continuously changed or when the amountof lift or working angle are changed.

Referring to FIG. 1, an electronic control unit (ECU) 31 is comprised ofa digital computer provided with components connected to each otherthrough a bi-directional bus 32 such as a RAM (random access memory) 33,ROM (read only memory) 34, CPU (microprocessor) 35, input port 36, andoutput port 37. The intake pipe 15 upstream of the throttle valve 18 isprovided with an air flow meter 40 for detecting the flow rate of air(intake gas) passing through the intake pipe 15. Further, the surge tank14 is provided with a pressure sensor 41 for detecting the pressure Pmof the air in the intake pipe part IM (below, referred to as the “intakepressure”). Further, the accelerator pedal 42 is connected to a loadsensor 43 for generating an output voltage proportional to the amount ofdepression of the accelerator pedal 42, while the throttle valve 18 isprovided with a throttle opening degree sensor (not shown) for detectingan opening degree of the throttle valve 18. The output signals of thesesensors 40, 41, and 43 are input through corresponding AD converters 38to an input port 36. Further, the input port 36 is connected to a crankangle sensor 44 generating an output pulse each time the crank shaftrotates by for example 30°. The CPU 35 uses the output pulse of thecrank angle sensor 44 to calculate the engine speed. On the other hand,the output port 37 is connected through corresponding drive circuits 39to the spark plugs 10, fuel injectors 11, step motors 17, and intakevalve drive system 22. These are controlled based on output from theelectronic control unit 31.

In the internal combustion engine of the present embodiment, the fuelinjection amount (fuel injection time) TAUi of an i-th cylinder (i=1, 2,. . . , 8) is for example calculated based on the following equation(1).TAUi=TAUb·ηi·k  (1)

Here, TAUb indicates the basic fuel injection amount (basic fuelinjection time), ηi indicates the air amount variation correctioncoefficient of the i-th cylinder, and k indicates another correctioncoefficient.

The basic fuel injection amount TAUb is the fuel injection amountrequired for making the air-fuel ratio match the target air-fuel ratio.This basic fuel injection amount TAUb is found in advance as a functionof the parameters relating to the engine operating conditions (forexample, the engine load, the engine speed NE, etc., below referred toas the “operating parameters”) and stored in the form of a map in theROM 34. Alternatively, it is calculated by an equation based on theoperating parameters. Further, the correction coefficient k expressesthe air-fuel ratio correction coefficient, acceleration increasecorrection coefficient, etc. combined together and is made 1.0 when nocorrection is needed.

If the amount of air filled in an i-th cylinder when the intake strokeis completed is referred to as the “cylinder air filling amount Mci(g)”,the air amount variation correction coefficient ηi is for compensatingfor variation in the cylinder air filling amount Mci among thecylinders. The air amount variation correction coefficient ηi of an i-thcylinder is for example calculated based on the following equation (2).ηi=Mci/Mcave  (2)

Here, Mcave indicates an average value of cylinder air filling amountsMci (=ΣMci/8. Here, “8” expresses the number of cylinders).

For example, if deposits comprised mainly of carbon are formed on theinner circumference of the intake pipe part IM or on the outercircumference of the intake valves 6, since the amount of deposition ofthe deposits will differ for each cylinder, the cylinder air fillingamount Mci is liable to vary among cylinders. Further, there issometimes manufacturing error among cylinders in the volumes of thecombustion chambers 5. In this case as well, the cylinder air fillingamount Mci is liable to vary among the cylinders. In the case where thecylinder air filling amount Mci varies among cylinders, if fuelinjection amounts are equal among all of the cylinders, the air-fuelratios or the output torques will vary among cylinders. Therefore, inthe present embodiment, the air amount variation correction coefficientηi is introduced to compensate for variations among cylinders in thecylinder air filling amount.

Note that, considering the fact that the timing at which fuel isactually injected is ahead of the timing of calculation of a fuelinjection amount TAUi by exactly a certain time, it is also possible tomake the basic fuel injection amount TAUb in equation (1) a predictivevalue advanced by exactly a certain time from the timing of calculationof the fuel injection amount TAUi by equation (1).

Alternatively, the fuel injection amount TAUi of an i-th cylinder can becalculated based on the following equation (3).TAUi=Mci·kAF·k  (3)Here, kAF is a correction coefficient for making the air-fuel ratiomatch with a target air flow ratio.

In this case as well, considering the fact that the timing when fuel isactually injected is ahead of the timing of calculation of the fuelinjection amount TAU by exactly a certain time, it is also possible tomake the cylinder air filling amount Mci in equation (3) a predictivevalue advanced by exactly a certain time from the timing of calculationof the fuel injection amount TAU.

In this way, both when calculating a fuel injection amount TAUi based onequation (1) and when calculating it based on equation (3), to make theair-fuel ratio match with the target air-fuel ratio for all of thecylinders so as to eliminate the variation of output torque among thecylinders, the cylinder air filling amount Mci has to be accuratelyfound.

In the present embodiment, a cylinder air filling amount Mci iscalculated based on the drop of the intake pressure Pm caused by theintake stroke of the i-th cylinder, that is, the intake pressure dropΔPmdwni. Next, the intake pressure drop ΔPmdwni will be explained whilereferring to FIG. 3 to FIG. 5.

FIG. 3 shows the intake pressure Pm detected by the pressure sensor 41at for example constant time intervals over 720° crank angle. The intakeorder in the internal combustion engine shown in FIG. 3 is#1-#8-#4-#3-#6-#5-#7-#2. In FIG. 3, OPi (i=1, 2, . . . , 8) is theintake valve opening/closing timing of an i-th cylinder, while a 0°crank angle expresses the intake top dead center of the #1 cylinder #1.As will be understood from FIG. 3, when a certain cylinder starts anintake stroke, the rising intake pressure Pm will start to fall andtherefore an upward peak will occur in the intake pressure Pm. Theintake pressure Pm falls further, then again rises and therefore adownward peak will occur in the intake pressure Pm. In this way, theintake pressure Pm is alternately formed with upward peaks and downwardpeaks. FIG. 3 shows the upward peaks and the downward peaks caused inthe intake pressure Pm due to the intake stroke of an i-th cylinder byUPi and DNi, respectively.

As shown in FIG. 4, if the intake pressure Pm at an upward peak UPi isreferred to as the maximum value Pmmaxi and the intake pressure Pm at adownward peak DNi is referred to as the minimum value Pmmini, the intakestroke of an i-th cylinder causes the intake pressure Pm to fall fromthe maximum value Pmmaxi to the minimum value Pmmini. Therefore, theintake pressure drop ΔPmdwni in this case is expressed by the followingequation (4):ΔPmdwni=Pmmaxi−Pmmini  (4)

On the other hand, as shown in FIG. 4, if the intake valve 6 starts toopen, the flow rate of air flowing out from the intake pipe part IM andsucked into a cylinder CYL, that is, the cylinder intake air flow ratemci (g/sec, see FIG. 5), starts to increase. Next, when the cylinderintake air flow rate mci becomes larger than the flow rate of airpassing through the throttle valve 18 and flowing into the intake pipepart IM, that is, the throttle valve air passage flow rate mt (g/sec,see FIG. 5), the intake pressure Pm starts to drop. Next, when thecylinder intake air flow rate mci drops and becomes smaller than thethrottle valve air passage flow rate mt, the intake pressure Pm startsto increase.

That is, air flows into the intake pipe part IM through the throttlevalve 18 by exactly the throttle valve air passage flow rate mt, andflows out from the intake pipe part IM through each intake valve 6 byexactly the cylinder intake air flow rate mci when air is taken into thei-th cylinder. In consideration of the above, the amount of outflow,that is, the cylinder intake air flow rate mci, temporarily exceeds theamount of inflow, that is, the throttle valve air passage flow rate mt,so the pressure inside the intake pipe part IM, that is, the intakepressure Pm, falls by exactly the intake pressure drop ΔPmdwni.

Now, the cylinder air filling amount Mci is the cylinder intake air flowrate mci integrated over time. Therefore, by ignoring the effect ofoverlap of the intake valve opening/closing timing OPi on the cylinderair filling amount Mci or air amount variation correction coefficient 71(see FIG. 3), the cylinder air filling amount Mci can be expressed bythe following equation (5). $\begin{matrix}{{Mci} = {{\int_{tmaxi}^{tmini}{( {{mci} - {mt}} ){\mathbb{d}t}}} + {{mt} \cdot \frac{{\Delta\quad{tdwni}} + {\Delta\quad{toc}}}{2}}}} & (5)\end{matrix}$

Here, tmaxi indicates the timing when an upward peak occurs in theintake pressure Pm, that is, an upward peak generation timing, tminiindicates the timing when a downward peak occurs in the intake pressurePm, that is, a downward peak generation timing, Δtdwni indicates thetime interval (sec) from the upward peak generation timing tmaxi to thedownward peak generation timing tmini, and Δtoc indicates the intakevalve opening time (sec) (see FIG. 4).

In equation (5), the right side first term expresses the area of thepart shown by T1 in FIG. 4 (below, referred to as the “region T1”), thatis, the area of the part surrounded by the cylinder intake air flow ratemci and the throttle valve air passage flow rate mt. The right sidesecond term expresses the area of the part shown by T2 in FIG. 4 (below,referred to as the “region T2”), that is, the area of the partsurrounded by the cylinder intake air flow rate mci, the throttle valveair passage flow rate mt, and the line mci=0, approximated by atrapezoid.

As explained above, due to an intake stroke being performed, thecylinder intake air flow rate mci temporarily exceeds the throttle valveair passage flow rate mt. Therefore, the cylinder air filling amount Mciobtained by integrating the cylinder intake air flow rate mci over timeexceeds the time integrated value of the throttle valve air passage flowrate mt. The region T1, in this way, expresses the excess of thecylinder air filling amount Mci with respect to the time integratedvalue of the throttle valve air passage flow rate mt occurring due to anintake stroke being performed.

Therefore, generally speaking, by dividing the cylinder air fillingamount into a first amount of air expressed by the area of the region T1(excess air amount) and a second amount of air expressed by the area ofthe region T2 (basic air amount), making the first amount of air theexcess of the cylinder air filling amount with respect to the throttlevalve air passage amount occurring due to an intake stroke beingperformed, and totaling the first amount of air and the second amount ofair for a cylinder, the cylinder air filling amount of the cylinder iscalculated.

On the other hand, the Law of the Conservation of Mass for the intakepipe part IM can be expressed by the following equation (6) using thestate equation for the air in the intake pipe part IM. $\begin{matrix}{\frac{\mathbb{d}{Pm}}{\mathbb{d}t} = {\frac{{Ra} \cdot {Tm}}{Vm} \cdot ( {{mt} - {mci}} )}} & (6)\end{matrix}$

Here, Vm indicates the volume (m³) of the intake pipe portion IM, Raindicates the gas constant divided by the average molecular weight ofair (below, referred to as simply as the “gas constant”), and Tmindicates the temperature (K) of the air in the intake pipe part IM (seeFIG. 5).

In the interval from the timing tmaxi to the timing tmini, the intakepressure Pm falls by exactly the intake pressure drop ΔPmdwni.Therefore, by expressing Vm/(Ra·Tm) by the parameter Km and expressingthe throttle valve air passage flow rate mt by the average value mtave,equation (5) can be rewritten using equation (6) to the followingequation (7). $\begin{matrix}{{Mci} = {{\Delta\quad{{Pmdwni} \cdot {Km}}} + {{mtave} \cdot \frac{{\Delta\quad{tdwni}} + {\Delta\quad{toc}}}{2}}}} & (7)\end{matrix}$

This being the case, if detecting the intake pressure Pm by the pressuresensor 41 to calculate the intake pressure drop ΔPmdwni, finding theabove-mentioned parameter Km, detecting the throttle valve air passageflow rate mt by the air flow meter 40 to calculate the average valuemtave, and detecting the timings tmaxi, tmini from the intake pressurePm and throttle valve air passage flow rate average value mtave tocalculate the time interval Δtdwni (=tmini-tmaxi), equation (7) can beused to calculate a cylinder air filling amount Mci. Note that intakevalve opening time Δtoc is stored in advance in the ROM 34.

However, as explained at the start, it is difficult to accurately findthe intake pipe volume Vm and intake pipe temperature Tm. Therefore, inthe present embodiment, the parameter Km is found without finding theintake pipe volume Vm and intake pipe temperature Tm. Next, a method forcalculation of the parameter Km of the present embodiment will beexplained while referring to FIG. 6A and FIG. 6B.

In the present embodiment, note should be taken of the amount of airflowing into the intake pipe part IM and the amount of air flowing outof the intake pipe part IM in a set crank angle range set so that atleast two cylinders for which the cylinder air filling amount Mci is tobe calculated are included.

FIG. 6A and FIG. 6B show the case where the 720° crank angle range inwhich the intake strokes of all cylinders are included, for example,from intake top dead center of the #1 cylinder to the next intake topdead center of the #1 cylinder, is set as the set crank angle range.

The total amount of air flowing into the intake pipe part IM within this720° crank angle range is expressed as the area of the part shown byhatching in FIG. 6A, that is, the product of the throttle valve airpassage flow rate average value mtave in this 720° crank angle range andthe required time t₇₂₀ required for the crank shaft to rotate by exactly720° crank angle (mtave·t₇₂₀). On the other hand, the total amount ofair flowing out from the intake pipe part IM to the insides of thecylinders in this 720° crank angle range is expressed as the area of thepart shown by hatching in FIG. 6B, that is, the total ΣMci of thecylinder air filling amounts Mci.

If the intake pressure Pm does not change much between the startingpoint and the end point in the 720° crank angle range, the total amountof air flowing into the intake pipe part IM in this 720° crank angle andthe total amount of air flowing out from the intake pipe part IM andfilled in each cylinder in this 720° crank angle should be substantiallyequal to each other. Therefore, in this case, the following equation (8)stands. $\begin{matrix}{{{mtave} \cdot t_{720}} = {\sum\limits_{i = 1}^{8}{Mci}}} & (8)\end{matrix}$

Entering equation (7) at the right side of equation (8) and cleaning itup, the parameter Km can be expressed as in the following equation (9).$\begin{matrix}{{Km} = {{mtave} \cdot \frac{{2t_{720}} - {\sum\limits_{i = 1}^{8}( {{\Delta\quad{tdwni}} + {\Delta\quad{toc}}} )}}{2{\sum\limits_{i = 1}^{8}{\Delta\quad{Pmdwni}}}}}} & (9)\end{matrix}$

That is, if calculating the throttle valve air passage flow rate averagevalue mtave from the throttle valve air passage flow rate mt detected bythe air flow meter 40, calculating the required time t₇₂₀ from theoutput of the crank angle sensor 44, calculating the total value ΣΔtdwniof the time interval Δtdwni (see FIG. 4) or the total valueE(Δtdwni+Δtoc) of the sum of the time interval Δtdwni and the intakevalve opening time Δtoc (see FIG. 4), and calculating the total valueΣΔPmdwni of the intake pressure drop ΔPmdwni, the parameter Km can becalculated. By doing this, the parameter Km can be simply found withoutfinding the intake pipe volume Vm and intake pipe temperature Tm,therefore a cylinder air filling amount Mci can be simply and accuratelyfound.

As shown in FIG. 7A and FIG. 7B, for example, it is also possible to seta 360° crank angle range in which the intake strokes of four cylindersare included as the set crank angle range. In the example shown in FIG.7A and FIG. 7B, a first 360° crank angle range from intake top deadcenter of the #1 cylinder to intake top dead center of the #6 cylinderand a second 360° crank angle range from intake top dead center of the#6 cylinder to the next intake top dead center of the #1 cylinder areset.

Regarding the first 360° crank angle range, the following equation (10)stands from the throttle valve air passage flow rate average value mtaveat the first 360° crank angle range, the required time t₃₆₀ required forthe crank shaft to rotate by exactly the first 360° crank angle range,and the total ΣMcj (j=1, 2, 3, 4) of the cylinder air filling amountsMcj of the cylinders which perform an intake stroke in the first 360°crank angle range. Here, j indicates the order of the intake strokes.Similarly, regarding the second 360° crank angle range, the followingequation (11) stands from the throttle valve air passage flow rateaverage value mtave′ at the second 360° crank angle range, the requiredtime t′₃₆₀ required for the crank shaft to rotate by exactly the second360° crank angle range, and the total EMcj (j=5, 6, 7, 8) of thecylinder air filling amounts Mcj of the cylinders performing an intakestroke in the second 360° crank angle range. $\begin{matrix}{{\sum\limits_{j = 1}^{4}{Mcj}} = {{mtave} \cdot t_{360}}} & (10)\end{matrix}$ $\begin{matrix}{{\sum\limits_{j = 5}^{8}{Mcj}} = {{mtave}^{\prime} \cdot t_{360}^{\prime}}} & (11)\end{matrix}$

Therefore, the parameter Km for the first crank angle range can beexpressed by the following equation (12), while the parameter Km for thesecond crank angle range can be expressed by the following equation(13). $\begin{matrix}{{Km} = {{mtave} \cdot \frac{{2\quad t_{360}} - {\sum\limits_{j = 1}^{4}( {{\Delta\quad{tdwnj}} + {\Delta\quad{toc}}} )}}{2\quad{\sum\limits_{j = 1}^{4}{\Delta\quad{Pmdwnj}}}}}} & (12)\end{matrix}$ $\begin{matrix}{{Km} = {{mtave}^{\prime} \cdot \frac{{2\quad t_{360}^{\prime}} - {\sum\limits_{j = 5}^{8}( {{\Delta\quad{tdwnj}} + {\Delta\quad{toc}}} )}}{2\quad{\sum\limits_{j = 5}^{8}{\Delta\quad{Pmdwnj}}}}}} & (13)\end{matrix}$

In this case, the cylinder air filling amounts Mcj (j=1, 2, 3, 4) of thecylinders performing an intake stroke in the first crank angle range arecalculated by equation (7) using the parameter Km calculated by equation(12), while the cylinder air filling amounts Mcj (j=5, 6, 7, 8) of thecylinders performing an intake stroke in the second crank angle rangeare calculated by equation (7) using the parameter Km calculated byequation (13).

Therefore, generally speaking, the set crank angle range is set so thatthe intake strokes of at least two cylinders for which the cylinder airfilling amount is to be calculated are included, the total valueΣΔPmdwni of the intake pressure drops ΔPmdwni of the cylindersperforming intake strokes in this set crank angle range is calculated,and the above-mentioned first amount of air is calculated based on theintake pressure drops ΔPmdwni and the intake pressure drop total valueΣΔPmdwni. Alternatively, it is also possible to view this as calculatingthe first amount of air based on the intake pressure drops ΔPmdwni,intake pressure drop total value FΔPmdwni, throttle valve air passageflow rate mt or its average value mtave, required time required for thecrank shaft to rotate by exactly the set crank angle range, timeinterval Δtdwni from when the intake pressure Pm generates an upwardpeak UPi (see FIG. 4) to when it reaches a downward peak DNi or itstotal value ΣΔtdwni, or intake valve opening time Δtoc or its totalvalue ΣΔtoc.

However, for example, if the intake valve opening/closing timing is setto the retarded side RT (see FIG. 2), the intake valve closing timing VCwill become the intake bottom dead center or later. In this case, evenif the piston starts to rise, the intake valve 6 is held in the openstate, so the air sucked into the cylinder is liable to flow back intothe intake pipe part IM. If this backflow occurs, as shown by X in FIG.8, the cylinder intake air flow rate mci will temporarily become anegative value and the region T2 can no longer be approximated by atrapezoid. That is, when there is backflow of air from inside a cylinderto the intake pipe part IM at the end of the intake stroke, the cylinderair filling amount Mci cannot be accurately calculated from equation(7).

Therefore, in the present embodiment, when the intake valveopening/closing timing is set at the retarded side RT, the action ofcalculation of a cylinder air filling amount Mci by equation (7) isprohibited. In this case, the cylinder air filling amount Mci is notupdated. The air amount variation correction coefficient ηi iscalculated from the cylinder air filling amount Mci calculated at theprevious calculation cycle.

FIG. 9 shows the routine for calculation of the fuel injection amountTAUi of an i-th cylinder of the present embodiment. This routine isexecuted by interruption every preset crank angle.

Referring to FIG. 9, at step 101, based on the engine load, the enginespeed, etc. detected by the load sensor 43, the crank angle sensor 44,etc., the basic fuel injection amount TAUb is calculated. Next, at step102, the routine for calculation of the cylinder air filling amount Mcishown in FIG. 10 is executed. Due to this, the cylinder air fillingamount Mci for a cylinder is calculated. Next, at step 103, based on thecylinder air filling amount Mci calculated at step 102 and the averagevalue Mcave of the cylinder air filling amount for all cylinders,equation (2) is used to calculate the air amount variation correctioncoefficient ηi of an i-th cylinder (i=1, 2, . . . , 8). Next, at step104, the correction coefficient k is calculated. Next, at step 105,based on the basic fuel injection amount TAUb, air amount variationcorrection coefficient ηi, and correction coefficient k calculated atsteps 101, 103, 104, equation (1) is used to calculate the fuelinjection amount TAUi. The fuel injector 11 of the i-th cylinder injectsfuel by exactly the fuel injection amount TAUi.

FIG. 10 shows the routine for calculation of the cylinder air fillingamount Mci of an i-th cylinder in the present embodiment.

Referring to FIG. 10, at step 121, it is judged if the opening timing ofthe intake valve 6 is set at the advanced side AD (see FIG. 2). When theopening timing of the intake valve 6 is set at the advanced side AD,next the routine proceeds to step 122 where the throttle valve airpassage flow rate average value mtave is calculated. Next, at step 123,the required time t₇₂₀ is calculated. Next, at step 124, the upward peakgeneration timings tmaxi and downward peak generation timings tmini foran i-th cylinder are detected (i=1, 2, . . . , 8). Next, at step 125,the time interval Δtdwni of an i-th cylinder is calculated(Δtdwni=tmini−tmaxi). Next, at step 126, Σ(Δtdwni+Δtoc) is calculated.Next, at step 127, the maximum values Pmmaxi and minimum values Pmminiof an i-th cylinder are detected. Next, at step 128, equation (4) isused to calculate the intake pressure drop ΔPmdwni for the i-thcylinder. Next, at step 129, the intake pressure drop total valueΣΔPmdwni is calculated. Next, at step 130, equation (9) is used tocalculate the parameter Km. Next, at step 131, equation (7) is used tocalculate the cylinder air filling amount Mci for an i-th cylinder. Asopposed to this, when at step 121 the opening timing of the intake valve6 is set at the retarded side RT, the processing cycle is ended.Therefore, calculation of the cylinder air filling amount Mci isprohibited.

In the embodiments explained above, the region T2 shown in FIG. 4 wasapproximated as a trapezoidal shape having a top side and a bottom sideof Δtdwni and Δtoc. However, the region T2 may also be approximated as arectangular shape with a side of for example Δtdwni. In this case, theabove-mentioned equations (7) and (9) become the following equations(14) and (15).Mci=ΔPmdwni·Km+mtave·Δtdwni  (14) $\begin{matrix}{{K\quad m} = {{mtave} \cdot \frac{t_{720} - {\sum\limits_{i = 1}^{8}{\Delta\quad{tdwni}}}}{\sum\limits_{i = 1}^{8}{\Delta\quad{Pmdwni}}}}} & (15)\end{matrix}$

Next, a second embodiment of the present invention will be explained.The equation (6) is modified as in the following equation (16) ifexpressing Vm/Ra as the parameter Km′. $\begin{matrix}{{{mt} - {mci}} = {\frac{K\quad m^{\prime}}{T\quad m} \cdot \frac{{\mathbb{d}P}\quad m}{\mathbb{d}t}}} & (16)\end{matrix}$

In the interval from the timing tmaxi to the timing tmini, the intakepressure Pm falls by exactly the intake pressure drop ΔPmdwni, so theequation (5) can be rewritten using equation (16) to the followingequation (17). $\begin{matrix}{{Mci} = {{\Delta\quad{{Pmdwni} \cdot \frac{{Km}^{\prime}}{Tm}}} + {{mt} \cdot \frac{{\Delta\quad{tdwni}} + {\Delta\quad{toc}}}{2}}}} & (17)\end{matrix}$

This being the case, if detecting the intake pressure Pm by the pressuresensor 41 to calculate the intake pressure drop ΔPmdwni, finding theabove-mentioned parameter Km′, detecting the throttle valve air passageflow rate mt by the air flow meter 40 to calculate the average valuemtave, and detecting the timings tmaxi, tmini from the intake pressurePm to calculate the time interval Δtdwni (=tmini−tmaxi), equation (17)can be used to calculate the cylinder air filling amount Mci. Note thatin equation (17), the intake valve opening time Δtoc is a valueinstructed from the ECU 31 to the intake valve drive system 22,therefore is the time when the intake valve 6 actually is open.

However, as explained at the start, due to the backflow of the airsucked into a cylinder to the inside of the intake pipe or otherfactors, if calculating the cylinder air filling amount as explainedabove, the cylinder air filling amount ends up including an error. Thatis, the right side second term of equation (17) approximates the regionT2 of FIG. 4 by a trapezoid. However, when backflow of air, etc.,occurs, the value calculated by approximation by the right side secondterm of equation (17) ends up greater than the region T2 by exactly theamount shown by the hatching in FIG. 11 and, as a result, the cylinderair filling amount is calculated greater and error ends up occurring. Inother words, if making the intake valve opening time Δtoc a value equalto the time when an intake valve 6 actually opens, the value calculatedby approximation by the right side second term of equation (17) will endup including error.

Therefore, in the present invention, by adjusting the intake valveopening time Δtoc to a suitable value rather than making it the timeduring which an intake valve 6 actually opens, even if air flows backetc., the region T2 can be calculated with a high precision. Below,while referring to FIG. 12A, FIG. 12B and FIG. 13, the method ofcalculation of the cylinder air filling amount in the present inventionwill be explained.

FIG. 12A and FIG. 12B show the cylinder air filling flow rate mci andthrottle valve air passage flow rate average value mtave for allcylinders in the crank angle 720° from intake top dead center of the #1cylinder to the next intake top dead center of the #1 cylinder.

The total amount of air flowing into the intake pipe part IM during thiscrank angle 720° is the area of the part shown by hatching in FIG. 12A,that is, is expressed by the product of the throttle valve air passageflow rate average value mtave during this crank angle 720° and therequired time t₇₂₀ required for the crank shaft to rotate by exactly thecrank angle 720° (mtave·t₇₂₀). On the other hand, the total amount ofair flowing out from the intake pipe portion IM and being filled intothe cylinders during this crank angle 720° is expressed as the area ofthe part shown by hatching in FIG. 12B, that is, the total ΣMci of thecylinder air filling amount Mci.

If the intake pressure Pm does not change much at all between thestarting point and end point of the crank angle 720°, during this crankangle 720°, the total amount of air flowing into the intake pipe part IMand the total amount of air flowing out from the intake pipe part IM andbeing filled into the cylinders should be substantially the same.Therefore, in this case, the following equation (18) stands.$\begin{matrix}{{{mtave} \cdot t_{720}} = {\sum\limits_{i = 8}^{8}{Mci}}} & (18)\end{matrix}$

Further, if entering equation (17) at the right side of equation (18)and cleaning it up, it can be expressed as the following equation (19).$\begin{matrix}{{{mtave} \cdot t_{720}} = {{\sum\limits_{i = 8}^{8}{\Delta\quad{{Pmdwni} \cdot \frac{K\quad m^{\prime}}{Tmave}}}} + {{mtave} \cdot \frac{{\sum\limits_{i = 1}^{8}{\Delta\quad{tdwni}}} + {\Delta\quad{{toc} \cdot 8}}}{2}}}} & (19)\end{matrix}$

Here, Tmave indicates the air temperature average value in the intakepipe part IM during a crank angle 720°.

However, equation (19) may not stand in practice. This is because, asexplained above, by making the intake valve opening time Δtoc a valueequal to the time for which an intake valve 6 actually opens, the rightside second term of equation (17) causes an error to arise in the valuecalculated by approximation.

Therefore, in the present invention, for the equation (19), the intakevalve opening time Δtoc is replaced by use of the variable x. In thiscase, the equation (19) is expressed as the following equation (20).$\begin{matrix}{{{mtave} \cdot t_{720}} = {{\sum\limits_{i = 8}^{8}{\Delta\quad{{Pmdwni} \cdot \frac{K\quad m^{\prime}}{Tmave}}}} + {{mtave} \cdot \frac{{\sum\limits_{i = 1}^{8}{\Delta\quad{tdwni}}} + {x \cdot 8}}{2}}}} & (20)\end{matrix}$

Further, by cleaning up equation (20) for the variable x, it can beexpressed as the following equation (21). $\begin{matrix}{x = {\frac{t_{720}}{4} - \frac{\sum\limits_{i = 1}^{8}{\Delta\quad{tdwni}}}{8} - {\frac{K\quad m^{\prime}}{Tmave} \cdot \frac{\sum\limits_{i = 1}^{8}{\Delta\quad{Pmdwni}}}{4 \cdot {mtave}}}}} & (21)\end{matrix}$

The thus calculated variable x is a value corresponding to the intakevalve opening time Δtoc and a value determined when assuming that thetotal amount of air flowing into the intake pipe part IM during thecrank angle 720° and the total amount of air flowing out from the intakepipe part IM and being filled in the cylinders during the crank angle720° are equal (below, referred to as the “virtual intake valve openingtime”). That is, the virtual intake valve opening time x is a value setso that the area of the part surrounded by broken lines in FIG. 13 (thatis, the trapezoidal part with a top side of Δtdwni, a bottom side of thevirtual intake valve opening time x, and a height of mtave) becomesequal to the area of the part surrounded by the cylinder intake air flowrate mci, the throttle valve air passage flow rate mtave, and the linemci=0 (region T2). However, FIG. 13 shows the case for one cylinder, butin actuality, the virtual intake valve opening time x is set so that thetotal value for all cylinders of the areas of the parts surrounded bythe broken lines becomes equal to the total value for all cylinders ofthe areas of the regions T2.

On the other hand, equation (17) becomes the following equation (22) byusing the variable x instead of Δtoc: $\begin{matrix}{{Mci} = {{\Delta\quad{{Pmdwni} \cdot \frac{K\quad m^{\prime}}{T\quad m}}} + {{mt} \cdot \frac{{\Delta\quad{tdwni}} + x}{2}}}} & (22)\end{matrix}$

Further, by entering the value of the variable x calculated by equation(21) into equation (22), the cylinder air filling amount of eachcylinder is accurately calculated.

That is, according to the present invention, a virtual intake valveopening time whereby the average air flow rate to all cylinders becomesequal to the throttle air passage flow rate is calculated. By using thevirtual intake valve opening time as the opening time of an intake valveto calculate the region T2, it is possible to accurately calculate thecylinder air filling amount to each cylinder.

FIG. 14 shows a routine for calculation of the cylinder air fillingamount Mci of an i-th cylinder according to a second embodiment. In thesecond embodiment, instead of the calculation routine shown in FIG. 10of the first embodiment, the calculation routine shown in FIG. 14 isused to calculate the cylinder air filling amount Mci of the i-thcylinder.

Referring to FIG. 14, at step 141, a throttle valve air passage flowrate mt is detected from the output of the air flow meter 40 etc. Next,at step 142, from the output of the pressure sensor 41, the upward peakgeneration timing tmaxi and downward peak generation timing tmini of theintake pressure due to the intake valve 6 of an i-th cylinder openingare detected (i=1, 2, . . . , 8). Next, at step 143, based on the peakgeneration timings tmaxi and tmini detected at step 142, the timeinterval Δtdwni of an i-th cylinder is calculated (Δtdwni=tmini−tmaxi).Next, at step 144, the calculation routine of the virtual intake valveopening time x shown in FIG. 15 is used to obtain the calculatedvariable x.

At step 145, from the output of the pressure sensor 41, the maximumvalue Pmmaxi and minimum value Pmmini of intake pressure due to theintake valve 6 of an i-th cylinder opening are detected. Next, at step146, based on the maximum value Pmmaxi and minimum value Pmmini detectedat step 145, equation (4) is used to calculate the intake pressure dropΔPmdwni of the i-th cylinder. At step 147, based on the output of atemperature sensor (not shown) etc., the temperature Tm of the intakepipe part IM is detected. Further, at step 148, based on the mt, Δtdwni,x, ΔPmdwni, and Tm calculated at steps 141, 143, 144, 146 and 147,equation (22) is used to calculate the cylinder air filling amount Mcito a cylinder. The calculated cylinder air filling amount Mci to acylinder is used for calculation of the fuel injection amount TAUi tothe cylinder shown in FIG. 9.

FIG. 15 shows the routine for calculation of the variable x according toan embodiment of the present invention. This calculation routine isperformed each time the crank shaft rotates by 720°.

Referring to FIG. 15, at step 161, based on the output of the crankangle sensor 44 etc., the time t₇₂₀ required for the crank shaft torotate by 720° is calculated. Next, at step 162, from the output of theair flow meter 40 etc., the average value mtave of the throttle airpassage flow rate while the crank shaft is rotating by 720° iscalculated. Next, at step 163, the time interval Δtdwni calculated atstep 143 of FIG. 14 is totaled up for all of the cylinders to calculateEΔtdwni. At step 164, the intake pressure drop ΔPmdwni calculated atstep 146 of FIG. 14 is totaled up for all of the cylinders to calculateFΔPmdwni. Next, at step 165, based on the output of the temperaturesensor, the average value Tmave of the temperature in the intake pipepart IM is calculated. Next, at step 166, based on the t₇₂₀, mtave,ΣΔtdwni, ΣΔPmdwni, and Tmave calculated at steps 161, 162, 163, 164, and165, equation (21) is used to calculate the value of the variable x.

Note that as explained above, equation (21) is conditional on the intakepressure Pm not changing much between the starting point and end pointof the crank angle 720°, so it is preferable to calculate the cylinderair filling amount Mci only at the time of steady-state operation and tosuspend the calculation of the cylinder air filling amount Mci at thetime of a transitory operation where the intake pressure Pm easilyfluctuates between the starting point and end point of the crank angle720°. Here, the “steady-state operation” means for example the time ofoperation under an engine load or an engine speed which is substantiallyconstant, while the “transitory operation” means for example the time ofoperation under an engine load or an engine speed which fluctuates.

Further, in the above explanation, the present invention was applied tothe case where the intake valve opening/closing timing was set to theretarded side, an intake valve was open even after intake bottom deadcenter, and therefore the air sucked into a cylinder flowed back intothe intake pipe. However, the present invention can be applied not onlyto this case, but also for example the case where the intake valveopening/closing timing is set to the advanced side, an intake valveopens from before intake top dead center, and due to this air does notflow into the intake pipe even while the intake valve is open.

Note that while the present invention was explained in detail based onspecific embodiments, a person skilled in the art could make variouschanges, modifications, etc. without departing from the claims and ideaof the present invention.

1. A control system for an internal combustion engine provided with aplurality of cylinders, introducing air into an intake passage partextending from a throttle valve to an intake valve through the throttlevalve in exactly a throttle valve air passage amount, and dischargingair from the intake passage part through an intake valve in exactly acylinder air filling amount to fill a cylinder at the time of an intakestroke, wherein the cylinder air filling amount is divided into a firstamount of air and a second amount of air, the first amount of air beingan excess of a cylinder air filling amount with respect to a throttlevalve air passage amount occurring due to an intake stroke, wherein thecontrol system comprises an intake pressure drop detecting means fordetecting a drop in intake pressure occurring due to an intake strokebeing performed, for each cylinder, a first air amount calculating meansfor calculating the first amount of air for a cylinder based on itsintake pressure drop; a throttle valve air passage amount detectingmeans for detecting a throttle valve air passage amount; a second airamount calculating means for calculating the second amount of air for acylinder based on the throttle valve air passage amount; a cylinder airfilling amount calculating means for totaling the first amount of airand the second amount of air to calculate the cylinder air fillingamount for a cylinder; and a control means for controlling the enginebased on the cylinder air filling amount of the cylinder, and whereinthe first air amount calculating means sets a set crank angle range soas to include the intake strokes of at least two cylinders for whichcylinder air filling amounts are to be calculated, calculates the totalvalue of the intake pressure drop of the cylinders performing an intakestroke in the set crank angle range, and calculates the first amount ofair based on each intake pressure drop and the intake pressure droptotal value.
 2. A control system for an internal combustion engine asset forth in claim 1 wherein, when backflow of air from inside acylinder to the intake passage part occurs at the end of an intakestroke, the action of the second air amount calculating meanscalculating the second amount of air is prohibited.
 3. A control systemfor an internal combustion engine provided with a plurality of cylindersand a plurality of intake valves, wherein the cylinder air fillingamount to a cylinder is divided into a basic amount of air and an excessamount of air flowing from an intake passage part to the inside of thecylinder exceeding a throttle valve air passage flow rate due to openingof an intake valve, wherein the control system comprises a basic airamount calculating means for calculating a basic air amount based on athrottle valve air passage flow rate of air flowing into the intakepassage part through the throttle valve and the opening time of eachintake valve; an excess air amount calculating means for calculating anexcess air amount based on the drop in intake pressure due to opening ofsaid intake valve; a cylinder air filling amount calculating means fortotaling said basic air amount and excess air amount to calculate acylinder air filling amount to a cylinder; and a control means forcontrolling the engine based on the cylinder air filling amount to acylinder, and wherein said basic air amount calculating means calculatesa virtual intake valve opening time so that the average air flow rate toall cylinders becomes equal to the throttle air passage flow rate anduses said virtual intake valve opening time as the opening time of anintake valve.
 4. A control system as set forth in claim 3, wherein saidbasic air amount calculating means uses said virtual intake valveopening time as the opening time of an intake valve when backflow of airto the intake passage part occurs near the intake valve opening timingor near the intake valve closing timing.